In the treatment of thyrod cancer with radioactive iodine, it has been shown that low-dose ablation therapy (30 mCi 131I) is useful in subjects under age 40 years since 40% experience total ablation after one dose and at least 60% after two doses. Older subjects or those with aggressive cancer should receive 100 mCi 131I in order to achieve ablation more quickly. Additional patients with the syndromes of inappropriate secretion of TSH and postpartum thyroiditis hae been identified and are being studied to determine the pathogenesis of these disorders.